Condylar rotation and anterior translation in healthy human temporomandibular joints.

Mouth opening is achieved by a combined rotatory and translatory movement of the disc-condyle complex within the fossa. The aim of this investigation was to analyse the relationship between condylar rotation and anterior condylar translation during deliberate opening and closing movements. Three consecutive opening and closing movements were recorded by means of the opto-electronic system Jaws-3D in 61 individuals (28 females and 33 males), aged 12 to 76 years, without a past or present history of myoarthropathies of the masticatory system. The computer provided the numeric values as well as the plots of the movement of an intracondylar point in three planes and of the relationship between condylar rotation (opening angle, OA) and anterior translation (AT). The OA/AT curves were also analysed visually for differences in shape. A marked inter- and intraindividual (left/right) variability was found for the ratio between opening angle and anterior condylar translation. Visual analysis of the OA/AT curves allowed them to be classified into five main groups. The groups differed statistically with respect to maximum opening angle and maximum mouth opening. The two groups with a more pronounced rotatory component at the end of opening had a significantly larger mouth opening than most of the other groups.